Process for the production of sheet materials with reversible absorptivity for moisture vapor

ABSTRACT

A process for the production of sheet material having reversible absorptivity for moisture vapor by applying polymers containing at least 5% by weight of esters of ethylenically unsaturated carboxylic acids with tertiary alcohols having four to eight carbon atoms as polymerized units to substrate materials and heating to a temperature higher than the decomposition temperature of the polymer to thereby eliminate an olefin and form free carboxylic groups in the polymer.

United States Patent Gaeth et a1.

Dec. 2, 1975 PROCESS FOR THE PRODUCTION OF SHEET MATERIALS WITH REVERSIBLE ABSORPTIVITY FOR MOISTURE VAPOR Inventors: Rudolf Gaeth, Limburgerhof;

Friedrich Hoelscher, Ludwigshafen; Bernard Schmitt, Kirchzarten; Dieter Blum, Limburgerhof, all of Germany Badische Anilin- & Soda-Fabrik Aktiengesellschaft, Ludwigshafen (Rhine), Germany Filed: Jan. 2, 1973 Appl. No.: 320,261

Published under the Trial Voluntary Protest Program on January 28, 1975 as document no. B 320,261.

Related U.S. Application Data Continuation of Ser. No. 100,779, Dec. 22, 1970, abandoned.

Assignee:

Foreign Application Priority Data Dec. 30, 1969 Germany 1965587 U.S. Cl. 427/226; 427/340; 427/341; 427/342; 427/373; 427/381; 428/245; 428/310 Int. Cl. B05D 3/02 Field of Search 260/25 D; 1l7/l38.8 E,

ll7/l38.8 N, 135.5, 140 A. 161 UB, 161 UC. 62, 46 CA, 161 UT, 126 GB. 119.6; 427/373, 341. 342, 381, 340; 428/245. 310

[56] References Cited UNITED STATES PATENTS 2,754,280 7/1956 Brown et a1. 11.7/161 UB 2,961,332 11/1960 Nairn 117/11 3,044,970 7/1962 Baumeister et a1. 260/25 D 3,239,365 3/1966 Petty 117/11 3,310,422 3/1967 Petry 117/11 X 3,598,770 8/1971 Moore et a1. 117/140 A Primary ExaminerWilliam D. Martin Assistant Examiner-Theodore G. Davis Attorney, Agent, or Firm-Johnston, Keil, Thompson & Shurtleff [57] ABSTRACT A process for the production of sheet material having reversible absorptivity for moisture vapor by applying polymers containing at least 5% by weight of esters of ethylenically unsaturated carboxylic acids with tertiary alcohols having four to eight carbon atoms as polymerized units to substrate materials and heating to a temperature higher than the decomposition temperature of the polymer to thereby eliminate an olefin and form free carboxylic groups in the polymer.

13 Claims, No Drawings PROCESS FOR THE PRODUCTION OF SHEET MATERIALS WITH REVERSIBLE ABSORPTIVITY FOR MOISTURE VAPOR This is a continuation of application Ser. No. 100,799, filed Dec. 22, l970. and now abandoned.

The invention relates to a process for the production of sheet materials having reversible absorptivity for moisture vapor by applying a polymer containing ester groups from tertiary alcohols to a substrate such as mats of fibers or woven or nonwoven fabrics. and heating the sheet material so that the polymer expands to form a foam material.

Materials which come into contact directly or indirectly with the human body, such as clothing. footwear or upholstery materials and the like, should be breathable" so that they do not give an unpleasant cold sensation at low temperatures and do not cause unpleasant perspiration at high temperatures. Many sheet materials made from natural substances such as wool, cotton. leather and the like do breathe and consequently have agreeable wearing properties.

This important property is present in only an unsatisfactory degree in synthetic sheet materials such as artificial leather.

In order to achieve breathability it is not sufficient to make such sheet materials permeable to gas, as has very often been attempted in industry. Synthetic fiber materials, for example. are gas permeable. Natural materials breathe because they have the desirable capacity for binding moisture vapor (and releasing it again) sufficiently quickly. A measure of breathability is accordingly the absorption of moisture vapor per square meter of surface of the leather or artificial leather in g/kg. The problem of making artificial leather breathable has not been solved to an adequate extent as may be seen from the following Table l:

The synthetic leathers (A to D) are products already widely used as shoe upper materials. The natural leathers (E side leather. F sole leather) are commercial grades.

The present invention has for an object to provide synthetic sheet materials which are capable of breathing. Another object of the invention is the provision of porous sheet materials which are air permeable. Other objects and advantages of the invention will be evident from the following description and the Examples.

These objects are achieved by applying to a substrate material a polymer containing at least 5% by weight of units of an ester of an ethylenically unsaturated carboxylic acid with a tert-butyl alcohol and heating to a temperature which is higher than the decomposition temperature of the tert-butyl ester groups.

When the polymers are heated, they decompose with the elimination of an olefin. for example isobutylene, so that free carboxylic groups are formed in the polymers. Expansion of the polymer by the eliminated olefin takes place at the same time. The necessary large internal surface area is thus formed and this effects an adequately rapid absorption of moisture vapor.

In all cases there is the problem of combining the substrate (which should have the necessary strength values such as tear and tensile strengths) as uniformly as possible with the polymer. Consequently the process may be carried out most simply in practice by using the polymers in finely divided form, most conveniently in the form of aqueous dispersions or as fine powders or solutions.

The preferred aqueous dispersions of the polymers conveniently contain from 20 to preferably from 25 to 55%, of polymer.

The polymers contain at least 5% and preferably more than 20% of tert-butyl ester in polymerized form. Suitable tert-butyl esters are those of cthylenically unsaturated carboxylic acids which are polymerizable or copolymerizable and which contain three or four carbon atoms, such as acrylic acid. methacrylic acid or maleic acid.

As comonomers which together with the said unsaturated esters of tertiary alcohols may build up the polymers. copolymerizable cthylenically unsaturated compounds are suitable, examples being acrylic or methacrylic esters of alcohols having one to nine carbon atoms, vinyl esters, vinyl chloride, vinylidene chloride. styrene, butadiene and the like.

Dispersions of polymers which contain units of carboxylic esters of tertiary alcohols and or copolymerizable acids which have a dissociation constant of more than 10 are particularly advantageous for the process according to the invention. Vinylsulfonic acid is preferred as a copolymerizable acid having a dissociation constant of more than 10 Examples of other acids which may be used are styrenesulfonic acid. 3-mcthacryloxypropylsulfonic acid, 3-methacryloxyethylsulfonic acid, 3-acryloxypropylsulfonic acid, 3-acrylox yethylsulfonic acid and vinylphosphonic acid. The content of such units of acids in the copolymers may be from 0.1 to 10%. preferably from 0.5 to 5%. by weight based on the total amount of monomers.

It may also be emphasized that the inclusion of 0.5 to 20% by weight (based on the whole amount) of units of monomers having strongly polar groups such as acrylic acid or acrylonitrile offers advantages. The polymer dispersions may be prepared by conventional methods by polymerization of monomers in aqueous phase with conventional systems of assistants. Polymers to be used according to the invention have a K value (according to Fikentscher) which is higher than 25.

Preferred substrates are sheet materials which are permeable to gases. Fiber substrates such as nonwoven. woven or knitted fabrics are particularly suitable. Felts and narrow-mesh netting are also suitable. The fibers may be of organic or inorganic nature. Webs of expanded material having mainly open cells or perforations (pores) are also suitable, for example expanded polyolefin materials.

Substrate materials made from synthetic polymers are particularly suitable. The dispersions may be applied to the substrates for example by dipping. brushing, pouring, spraying or impregnation. The polymers may also be rolled onto the substrates.

According to a particularly advantageous embodiment of the process, the substrate is impregnated with the aqueous dispersions of the polymer and the water is first evaporated at a temperature lower than the de composition temperature of the polymer containing tertiary ester groups. i.e.. lower than the temperature at which the olefin is eliminated. The sheet material thus obtained is then heated to a temperature above the decomposition temperature of the polymer so that decomposition takes place. This process may be carried out at atmospheric. subatmospheric or superatmospheric pressure. for example in a press. In the latter case a smooth or grained surface is immediately obtained depending on the surface of the plates. When atmospheric pressure is used. the surface is somewhat uneven. It can be buffed flat by known methods however. for example on a leather buffing machine. When subatmospheric pressure is used. propellant gas formed during the expansion process is removed particularly quickly.

The acid groups exposed by the decomposition process are advantageously at least partly neutralized. for example converted into their sodium salt. because absorption of moisture vapor and the desired breathing effect are thus increased. After neutralization has been carried out (advantageously in aqueous phase) the product is washed. dried and then treated by a conventional method. for example a top coat is applied. Neutralization may also be carried out with gaseous ammonia. in which case the washing step may be omitted.

The decomposition temperature of the carboxylic esters is the temperature at which the units of carboxylic ester in the polymer are converted into carboxylic acids and olefins. The decomposition temperature is determined by various factors. for example the type of carboxylic ester used or its concentration in the polymer. The decomposition temperature has to be ascertained in each case.

The decomposition of polymers having ester groups from tertiary alcohols in aqueous dispersions or solutions is also dependent on the pH. It is therefore advantageous to set up a pH of 1.5 or less prior to the decomposition process. It is advantageous to use a pH range of from 1.5 to 0.1. Particularly finely cellular foams are thus formed which enable the moisture vapor to be absorbed sufficiently rapidly. The step of setting up a low pH makes it possible to carry out the decomposition process at from 70 to 170C without the time required therefor being more than 30 minutes. The low pH is set up by adding sulfuric acid. phosphoric acid. benzenesulfonic acid. toluenesulfonic acid or compounds which liberate acids.

The temperature and duration of heating to be used advantageously in any case depend on the thermal resistance of the substrate (fiber mat or woven. nonwoven or knitted fabric) and on the composition of the polymers used for the coating and any other additional materials used. The most advantageous temperature is usually within the range from 70 to 170C. preferably from 100 to 140C. and the duration of the heating is usually within the range from 30 seconds to 30 minutes. preferably from 2 to 15 minutes.

We have found it expedient to add to the polymers containing tertiary ester groups polyfunctional compounds which will react with the acid groups exposed by the decomposition process. Examples are polyfunctional alcohols such as glycerol and glycol. The resultant crosslinking reaction imparts to the sheet material 4 a higher resistance to the action of water so that when the sheet materials are left in water they swell up but do not disintegrate. These compounds may be added in amounts of from 0.5 to 607r. preferably 3 to 2571. by weight based on the amount of polymer used.

To increase the resistance of the sheet materials to the influence of water it is also possible (after the decomposition process has been carried out) to react the carboxyl groups of the polymerized foam with a polyfunctional compound. for example with a polybasic amine. isocyanate or polyvalent metal ions such as aluminum. chromium or calcium ions.

Provided that sheet materials are to be prepared up to a weight of about 100 g/m" using dispersions of the said polymers. the use of dispersions in the conventional viscosity range is adequate. lf higher weights per m are to be prepared however. i.e.. thicker plies. as for example synthetic leather sheeting capable of absorbing moisture vapor which is suitable for shoe soles and shoe uppers. it is difficult. to impregnate the substrate materials with the necessary amount of dispersion homogeneously so that an adequate amount of dispersion is applied prior to drying. It has proved to be advantageous to add to the dispersion a substance which causes the dispersion to coagulate when the temperature of the dispersion is raised above about 50C. Such substances which cause thermal sensitivity are known. an example being polyvinyl methyl ether. For example 1 to 50 parts. preferably 3 to 10 parts. of polyvinyl methyl ether may be used for each 100 parts of the polymer to be used according to the invention. The procedure in this method is advantageously that after impregnation and if possible on the support on which the nonwoven fabric has been laid prior to impregnation. the coated material is heated for about 5 to 60 seconds at a temperature of from 50 to 200C. In this way the dispersion is coagulated on the substrate; the whole structure has thus become transportable in the moist condition and can be supplied to the drying process. After it has been dried, the dispersion is then thermally decomposed and further processed as already de-- scribed. Heating is advantageously carried out by means of a heat carrier. This may be sheet metal. for example iron sheet. which is in direct contact with the coated structure.

Breathable sheet materials prepared in this way have to have the necessary flex durability for use as upholstery and clothing materials. When they have absorbed moisture vapor. the water bound by the polymers has a softening effect. When such products are dried out completely, the sheet material may become fairly stiff if the binder does not itself have the necessary degree of softness. To prevent this effect it is convenient either to use polymers which by themselves. for example as a result of conventional plasticization. have the necessary flexibility even in the completely dry condition. or (as is customary in the case of leather) to add humectants. as for example polyhydric alcohols. glycol. glycerol. pentaerythritol. polyethylene oxide. polypropylene oxide and the like. The amount added is conveniently from 5 to 40% of the weight of the polymer. It is advantageous to use compounds which have such a high molecular weight that evaporation cannot take place to such an extent that the softening effect will be lost in the course of time.

The desired breathability of the sheet materials is achieved because moisture vapor can be bound due to the hydrophilic nature of the binder and the absorption of moisture vapor can take place quickly because of the adequately large internal area. These two basic conditions are satisfied by natural materials. For example leather has a very large internal surface area due to the natural fibrillar structure.

Articles of clothing and upholstery material breathe if they are capable of lowering humidity between the body and the article of clothing to such an extent that water cannot occur in liquid phase. Basically, three different requirements have to be fulfilled:

1. In the case of textiles, for example shirts, the moisture vapor has to be taken up so quickly by the cloth that the necessary lowering of the moisture vapor concentration between the body and the cloth takes place. At the same time the water absorbed in this way is able to evaporate continuously during wear on the side away from the body, so that it is not necessary for the cloth to retain a certain minimum amount of water while it is being worn.

2. In the case of shoe-upper material the situation is rather different because the dressing substantially prevents evaporation of water on the side removed from the body while the shoes are being worn. All of the material must therefore bind moisture vapor at adequate speed and during wear should retain a certain quantity of water.

3. In the case of upholstery leather the dressed side is in contact with the body. It is therefore necessary either to ensure that the dressed side itself has adequate absorptivity for moisture vapor or is perforated to an adequate extent to ensure that the water-absorptive layer lying beneath it is in direct contact with the ambient atmosphere saturated with moisture vapor.

Consequently smaller amounts of the appropriate polymers are required for the first application while in the second and third applications larger amounts and 4 therefore higher weights per m are required.

By the process described it is possible to prepare sheet materials for example artificial leather, which have substantially higher moisture absorptivity than natural leather. Thus for example when using polymerized tert-butyl acrylate by the abovementioned process. sheet materials can be prepared having a moisture vapor absorptivity of more than 400 g/m at a thickness of 1 mm.

As may be realized from what has been said above, it

I is only possible to make general statements regarding the amount ofpoly'mer which it is advantageous to apply to the substrate materialsowing to the various embodiments of the subject of the invention. ln the case of artificial leather it is advantageous, but not essential, to use (with reference to 1 part by weight of substrate material) from 0.5 to 5 parts by weight of the polymer to be used according to the invention, i.e'., the polymer containing ester groups from tertiary alcohols. It is advantageous, however, to use I to 2 parts of polymer for each part by weight of substrate material.

In the case of the production of textile sheet materials, which may be used for example as clothing materials, considerably lower amounts of polymer may be used with reference to the substrate material. Thus for example it may be advantageous to apply from 2 to 6 it is possible however to adjust a-whole series of other important properties such as resistance to cold, attri' tion and so forth. to' the desired level by combining the polymers to be used according to theinvention with other polymers. This can be achieved most simply by adding to the aqueous polymer dispersions, other aqueous dispersions and carrying out the process with the resultant mixtures. For example a dispersion of a copolymer of butyl acrylate may be mixed with a dispersion based on polyvinylidene chloride, polyvinyl chloride, polyacrylic esters, polymethacrylic esters, polyvinyl esters, polydienes and the like. It is also possible. however, to prepare these polymer mixtures-by adding powdered polymers to the aqueous dispersions. This is particularly convenient where it is difficult to prepare the other polymers in the form of a dispersion, for example in the case of polyolefins. The procedure in this case may be that'polyethylene powder is added to the dispersed copolymer containing ester groups from tertiary alcohols, uniformly dispersing it therein and then following the procedure described above for the production of sheet materials having moisture vapor absorptivity. i

Naturally it is also possible to disperse'the added polymer in the form of a solution into an aqueous dispersion. This is of interest for example when a polymer is to be incorporated which (a) can only be prepared in dispersion with difficulty but (b) is so soft that preparation of the powder presents difficulties. This is the case for example with polyisobutylene which is conveniently incorporated into the dispersions by way of a solution in an aliphatic hydrocarbon. It is generally advantageous to use such an amount of the other polymer that there is 0.1 to 10, preferably 0.5 to 2. parts of other polymer to 1 part of the polymer to be used according to the invention.

Naturally it is also possible to add to the polymers other additives such as fillers, dyes, fungicides, flame retardants, finely ground other expanded plasticsfshort fibrous materials such as asbestos, or cut fibers up to 30 mm length. but preferably less than 0.5 mm. Depending on their properties, particularly as regards the substrate v materials used and the binder combinations, the sheet materials may be used for applications'in which moisture absorptivity and release are important. This is the case in the whole range of clothing, although the level of moisture absorptivity may vary considerably.

v In the manufacture of artificial leather for shoe uppers there is the problem of imparting to thematerial the property of binding at least the same amount of moisture vapor as natural leather. Practically the whole of-the moisture vapor must be retained by the artificial leather as there is only slight evaporation on the side facing away'from the body, this being the dressed side moisture vapor can be released during wear on the side parts by weight of polymer with reference to 100 parts facing away from the body. Such materials include clothing materials, e.g., shirting, where a much lower moisture absorptivity (from 30 to 50 g/m is adequate. The substrate, by absorbing moisture vapor on the side which is in contact with the body and releasing it again on the other side, keeps the moisture vapor concentra- 7 tion at a level where the formation of droplets (perspiration) is avoided.

The invention is further illustrated by the following Examples in which parts and percentages are by weight.

EXAMPLE 1 l m'- of a nonwoven fabric made of split fibers of polypropylene and having a fraction of 24% which is soluble in n-heptane and a weight of 600 g/m' is impregnated with a 28% liquor having the following composition:

150 parts of a 40% emulsion polymer of tert-butyl acrylate;

9.5 parts of 10% sulfuric acid:

3 parts of a 20% solution of an oxyethylated fatty alcohol:

24 parts of a aqueous solution of polyvinyl methyl ether; and

50 parts of water which is necessary to achieve a viscosity suitable for impregnation. The liquor has a pH of l.

The fabric which has been soaked is lightly squeezed and brought into contact for a few seconds with metal surfaces having a temperature of 150C so that partial coagulation of the impregnated material takes place. This treatment results in a sheet material which it is easy to handle.

The material is dried at 75C and then treated in a press for 30 minutes at 150C and atmospheres gauge. then kept in 5% sodium bicarbonate solution. washed thoroughly. dried in the air and conditioned at 23C and 50% humidity.

The sheet material obtained is exposed to an atmosphere having a humidity of 100%.

The absorption of moisture vapor is determined after 1. 2. 8 and 12 hours. The absorption of moisture vapor is given in Table 2 in g/m and mm thickness and in g/kg.

The sheet material is accordingly superior in water absorption to the artificial leather tested and approximately reaches the level of both types of leather when the amount of moisture vapor absorbed is related to area and thickness of the layer; when related to the weight of the sheet material however it is clearly supenor.

EXAMPLE 2 1 m of a nonwoven fabric made of split fibers of polypropylene and having a fraction of 24% which is soluble in n-heptane and a weight of 600 g/m is impregnated with a 25% liquor having the following composition:

150 parts of a 40% emulsion polymer of tert-butyl acrylate; 6.5 parts of 10% sulfuric acid; and 2.5 parts ofa 20% aqueous solution of an oxyethylated fatty alcohol. The liquor has a pH of l.

A mixture of 72.5 parts of a 55% dispersion of an emulsion polymer from 91 parts of vinylidene chloride and 9 parts of methyl acrylate and 2.5 parts of a 20% aqueous solution of an oxyethylated fatty alcohol is added and the whole is adjusted to pH 1 with aqueous sulfuric acid.

The mixture of the dispersions is diluted with 50 parts of water and then 45 parts of a 15% aqueous dispersion of polyvinyl methyl ether having a K value of 45 is added. The mixture is diluted by adding 100 parts of water so that its viscosity permits satisfactory impregnation. Sheet material is prepared from the impregnated fabric in the manner described in Example 1.

Absorption of moisture vapor of the finished sheet material after 1. 2. 8 and 12 hours is determined and is reproduced in Table 2.

EXAMPLE 3 l m of a nonwovenfabric made of split fibers of polypropylene. having a fraction soluble in n-heptane of 24% and weighing 600 g/m". is impregnated with a 35% aqueous liquor having the following composition:

250 parts of an emulsion polymer (from 93 parts of tert-butyl acrylate. 4 parts of methyl acrylate and 3 parts of acrylonitrile) is adjusted to pH 1 with 40 parts of 30% phosphoric acid which contains 5 parts of a 20% aqueous solution of an oxyethylated fatty alcohol. Then 40 parts of a 15% aqueous solution of a polyvinyl methyl ether is added.

Sheet material is prepared as described in Example 1.

Absorption of water vapor by the finished sheet material after 1. 2. 8 and 12 hours is determined and is reproduced in Table 2.

EXAMPLE 4 1 m of a nonwoven fabric made of split fibers of polypropylene and having a fraction of 24% which is soluble in n-heptane and a weight of 600 g/m is impregnated with a 25.5% liquor having the following composition:

150 parts of a 40% emulsion polymer of tert-butyl acrylate and 3 parts of a 20% aqueous solution of an oxyethylated fatty alcohol are mixed. The mixture has a pH of 1. 4

24 parts of a 15% aqueous solution of a polyvinyl methyl ether is then added.

After the mixture has been homogenized and the originally highly viscous mixture has been diluted with parts of water, production of sheet material as described in Example 1 can be carried out.

Moisture absorptivity of the finished sheet material is determined after 1 hour, 2, 8 and 12 hours. The results are reproduced in Table 2.

EXAMPLE 5 l m of a needle-punched web of polycaprolactam (nylon 6) weighing 200 g/m'- is impregnated with a 25% liquor of the following composition:

Mixture 1: 150 parts of a 40% aqueous emulsion copolymer of 93 parts of tert-butyl acrylate, 4 parts of methyl acrylate, 2 parts of vinylsulfonic acid, 3 parts of acrylic acid and 2.5 parts of a 20% solution of an oxyethylated fatty alcohol.

Mixture 2: 72.5 parts of a 55% emulsion copolymer of 91 parts of vinylidene chloride and 9 parts of methyl acrylate isadjusted to pH 1 with a mixture of 5 parts of 10% sulfuric acid and 2.5 parts of a 20% aqueous solution of an oxyethylated fatty alcohol.

The two mixtures are mixed and diluted with 50 parts of water and then 40 parts of a 15 aqueous solution of polyvinyl methyl ether is added. The mixture is ho-' mogenized and the highly viscous mixture is diluted with parts of water; it then has a consistency suitable for impregnation and further processing is carried out as described in Example 1.

Moisture absorptivity of the finished sheet material after 1 hour, 2. 8 and 12 hours is determined and repro- EXAMPLE 6 l m of nonwoven polycaprolactam (nylon 6) fabric weighing 200 g/m is impregnated with a 27% liquor having the following composition:

10 for further processing into sheet material as described in Example 1.

Moisture absorptivity of the finished sheet material is determined after 1 hour, 2, 8 and 12 hours and given in Table 2.

In Table 2, E1 to E7 sheet material according to Examples 1 to 7; and A/B and A/D artificial leathers A/B and A/D.

TABLE 2 Absorption of moisture vapor after the following hours:

per mll mm thick g/kg El 25 40 70 90 70 110 210 250 E2 20 30 40 50 90 135 105 E3 20 35 00 75 50 95 170 210 E4 20 35 8O )0 61) 101) 220 251) E5 120 175 315 3x0 120 1x0 320 3140 E6 135 195 350 425 1-10 200 361) 430 E7 1 10 160 300 355 120 180 330 380 Mixture 1: 150 parts of a 40% a ueous emulsion 01- q p EXAMPLE 8 ymer from 93 parts of tert-butyl acrylate, 4 parts of methylacrylate, 2 parts of vinylsulfonic acid and 3 parts of acrylic acid has added to it 2.5 parts of a 20% solution of an oxyethylated fatty alcohol and 10 parts of diglycol. The pH is 1.

Mixture 2: 72.5 parts of'a 55% emulsion copolymer from 91 parts of vinylidene chloride and 9 parts of methyl acrylate is adjusted to pH 1 with a mixture of 5 parts of 10% sulfuric acid and 2.5 parts of a 20% aqueous solution of an oxyethylated fatty alcohol.

The two mixtures are brought together while stirring and diluted with parts of water. 40 parts of a 15% aqueous solution of polyvinyl methyl ether is then added and the whole is homogenized. The mixture, which is originally very viscous, is diluted with 100 parts of water after which it has a consistency suitable for impregnation and further processing into sheet materials may be carried out as described in Example 1.

Moisture absorptivity of finished sheet material is determined after 1 hour, 2, 8 and 12 hours and shown in Table 2.

EXAMPLE 7 1 m of nonwoven polyamide (nylon 6) fabric having a weight of 200 g/m is impregnated with a 29% liquor having the following composition:

Mixture l: 150 parts of a 40% aqueous emulsion copolymer from 93 parts of tert-butyl acrylate, 4 parts of methyl acrylate, 2 parts of vinylsulfonic acid and 3 parts of acrylic acid has added to it 2.5 parts of a 20% solution of an oxyethylated fatty alcohol and 20 parts of diglycol. The pH is l.

Mixture 2: 72.5 parts of a emulsion copolymer from 91 parts of vinylidene chloride and 9 parts of methyl acrylate is adjusted to pH 1 with a mixture of 5 parts of 10% sulfuric acid and 2.5 parts of a 20% aque-' ous solution of a fatty alcohol.

The two mixtures are brought together while stirring Fabric from polypropylene strip is dipped into an about 45% aqueous dispersion of a copolymer of 89 parts of tert-butyl acrylate, 6 parts of vinylsulfonic acid and 5 parts of methyl acrylate having a K value of and a pH of 1.5 and then heated for about 5 minutes at 130C in a drying cabinet so that the coating expands.

When the expanded material is given a conditioning at 23C and 50% humidity for 24 hours and then exposed to an atmosphere saturated with water vapor. up to about 60% of water (with reference to the dry weight of the whole material) is absorbed in 24 hours. If the material is then placed in a standard climate, the absorbed moisture is given off again. This cycle can be repeated as often as desired.

10% by weight of silica gel may be added to the aqueous dispersion.

EXAMPLE 9 The procedure of Example 8 is followed but treatment is carried out with a 40% dispersion of a copolymer of 94 parts of tert-butyl acrylate, 2 parts of vinylsulfonic acid and 4 parts of methyl'acrylate (K value The foamed article is coated on both sides with a solution of 200 parts of a copolyamide from 120 parts of AH-salt (adipic hexamethylenediamine) and parts of caprolactam in 675 parts of methanol and 75 parts of water, to which parts of Z-ethylhexyl hydroxybenzoate has been added, and dried for 2 hours at 70C.

The sheet material thus coated has a similar capacity for absorbing and giving up water vapor as the foamed material obtained according to Example 8.

EXAMPLE 10 verted at C into a foamed material which behaves like the material in Example 8 as regards absorption and release of water vapor.

EXAMPLE 1 1 A tricot fabric of polyacrylonitrile fibers is coated with the polymer dispersion according to Example 8 by application with a roller and then treated as in Example 8. A breathable sheet material is again obtained.

The copolymer may be used in. a 20% solution in tetrahydrofuran instead of as a dispersion. The result is the same.

EXAMPLE 12 i A nonwoven fabric of polyglycol terephthalate fibers is impregnated with an about 3571 aqueous dispersion of a copolymer of 85 parts of tert-butyl acrylate. 2 parts of vinylphosphonic acid and 13 parts of methyl methacrylate (pH 1.5). dried at 40C and then irradiated with a 500 watt infrared radiator at a distance of 8 cm for minutes. A foamed sheet material is obtained having similar absorption and release of water vapor to those of the material in Example l.

EXAMPLE 13 A 50% aqueous dispersion of a copolymer of 94 parts of tertbutyl acrylate. 4 parts of methyl acrylate and 2 parts of vinylsulfonic acid has added to it (with reference to the solids content of the dispersion) of glycol. This dispersion is applied'to a polyamide web in such an amount that there is 1 part of polymer to 5 parts of polyamide fabric. The coated material is dried for 5 hours at C and then heated for 15 minutesat a temperature of 130C so that it expands. The resulting material is stored for an hour in an ammonia atmosphere.

EXAMPLE 14 An aqueous dispersion of a copolymer of 91 parts of tert-butyl acrylate. 4 parts of methyl acrylate. Sparts of acrylic acid and 2 parts of vinylsulfonic acid has added to it 157r by weight of 1.2-propanediol with reference.

to the solids content of the dispersion. The mixture obtained is brushed onto polyacrylonitrile cloth so that 1 part of polymer is present for 3 parts of cloth. The cloth treated in this way is dried for 1 hour at 30C and then heated for 15 minutes at 130C. A foamed sheet material is formed which is particularly resistant to the action of alkalies.

By repeating the said procedure but not adding the 1.2-propanediol. the material is easily destroyed by the action of alkalies of the same concentration.

EXAMPLE 15 A sheet material prepared according to Example 5 is cut up in the form of insoles. These insoles are placed in shoes worn by test persons for a period of 12 hours. During this period the soles absorb on a average from 400 to 500 g of moisture vapor per square meter of sole material. Pleasant wearing properties arereported by all the test persons. Within a further periodof 12 hours while the shoes are not being worn. the whole of the moisture is given up again.

EXAMPLE l6 Polypropylene nonwoven fabric is impregnated as described in Example 1 using aqueous dispersions of polymers whose composition'is given in the following Table 3. The impregnated fabric is dried as described. pressed while heating andthus processed into sheet material.

. A nonwoven glass fabric is impregnated with a The material obtained is exposed to an atmosphere having a humidity of 100% The absorption of water vapor after 12 hours is determined in g/kg. The results are given in Table 3, in which Pts parts by weight and WVA water vapor absorption in g/kg after 12 hours.

EXAMPLE 17 I 1 square meter of a nonwoven fabric of silk filaments having a fiber length of about 8 cm and a weight of 300 g/m is impregnated with a 25% liquor of a mixture of mixtures 1 and 2 described in Example l. The impregnated web is dried and processed into a sheet material as described in Example 1.

The water vapor absorption of this material is 350 g/kg after it has been lying for 12 hours in air having a humidity of 100%. i

A sheet material may be prepared in the same way using a nonwoven glass fabric having a weight of 300 g/m which has previously been washed with'dilute hydrochloric acid. The water vapor absorption inthis case is 300 g/m l EXAMPLE 18 An emulsion polymer as described in Example 1 is adjusted to pH 1.5 and dried to a fine powder at C.

This powder is mixed in a ratio by weight of 1:1 with asbestos fibers and made into a web having a weight of 400 g/m The web is pressed in a press at C and 20 atmospheres gauge to form a sheet material and then expanded at C outside the press. The water vapor absorption of the material thus obtained is 300 g/kg.

EXAMPLE 19 dispersion of poly(methyl acrylate) and dried.

A 30% dispersion of a copolymer of 85 parts of tertbutyl acrylate, 5 parts of acrylic acid and 10 parts of nbutyl acrylate. which has apl-l of 318. is applied to the fabric which is then dried and heated for a period of 10 minutes at to C. The sheetmaterial obtained has a water vapor absorption of 300 g/kg.

EXAMPLE 20 As described in Example 1 a web is impregnated with the copolymer dispersion described therein, dried and processed at 150C into a sheet material. which is then treated with dilute sodium bicarbonate solution so that 75% of the free carboxyl groups are neutralized/The remaining free carboxyl groups are neutralized with an aqueous solution of hexam'ethylenediamine. The material is kept at 150C for minutes. The water vapor absorption is the same as that of the material obtained according to Example 1 but the resistance to liquid water is considerably improved.

EXAMPLE 21 A mixture of 80 parts of distilled water. 0.1 part of the sodium salt of a disulfonimide of a kerosene (C H 0.1 part ofa polyvinylpyrrolidone having a K value of 90. 0.3 part of benzoyl peroxide and parts of tert-butyl acrylate is prepared while stirring in a three-necked flask having a thermometer, reflux eondenser and blade stirrer. While stirring at a rate of 200 rpm. the mixture is brought to 70C and kept for 6 hours at this temperature and this stirring speed. After the whole has been cooled to about C. the suspended material is suction filtered, washed 3 times with distilled water and then dried at C in a vacuum cabinet. 19.0 parts of poly(tert-butyl acrylate) is obtained as a free-flowing powder.

100 parts of chrysotile asbestos having a fiber length of 1 mm is treated with 400 parts of 5% hydrochloric acid for 1 hour at C. The fibers are then filtered off and rinsed twice. each time with 1.000 parts of cold water and dried. The fibers pretreated in this way are introduced with 200 parts of the poly(tert-butyl acrylate) powder into an open blade type mixer and uniformly distributed. Then. while the mixer is still running. 20 parts of a 20% solution of a-naphthalene-sulfonic acid in water is sprayed in and the whole is mixed for another 15 minutes. After the whole has been homogeneously distributed. the mixture is dried to a moisture content of 1.5% in a loose layer on a lattice at 50C in a fresh air kiln. v

The homogeneous mixture is brought on a rolling mill (whose working roller is heated to 100C and whose pressure roller is cooled to 18C) to a layer thickness of 0.5 mm and the rolled sheet obtained is removed.

Four such layers are laid on each other at right angles and pressed at 100C for 15 minutes under a pressure of 3 kg/cm and then heated at 160C for 30 minutes with the pressure removed.

A porous sheet material is obtained having an average thickness of 6 mm. The water absorption of this material is l 80 g/kg after lying for 24 hours at 23C and l007r humidity.

EXAMPLE 22 700 parts of a mixture of 630 parts of ethyl acetate and parts of tert-butyl acrylate is brought to a refluxing temperature of 79 to C while stirring in a threenecked flask fitted with a thermometer, blade-type stirrer and supply vessel. Then 1.73 parts of benzoyl peroxide (dissolved in 10 parts of tert-butyl acrylate) is added. After the start of the polymerization (after about 30 minutes) a start is made in feeding in over a period of 5 hours a mixture of 650 parts of ethyl acetate and 785 parts of tert-butyl acrylate to the polymeriza- 14 tion mixture at 80 to 81C while stirring. When the whole has been added. 0.] part of benzoyl peroxide (dissolved in 5 parts of tert-butyl acrylate) is added and the reaction mixture is stirred for another 8 hours at 79 to 80C. and then cooled to 25C. 1.950 parts of a pale yellowish solution is obtained. Determination of the dissolved polymer gives a yield of 98 by weight (after drying for 6 hours in vacuo at 60C). The l\' value of the solution is 36.0 19? in ethyl acetate): the viscosity of the solution in DlN cup 4 at 20C is 6-1 seconds.

parts of this solution is homogeneously mixed with 1.0 part ofphosphoric acid having a density of 1.7 in a blade type mixer. While the mixer is still running. 80 parts of glass fibers having a mean thickness of 6 microns and which have been cut to a length of about 20 mm are scattered thereon and at the same time 80 parts of ethyl acetate .is slowly added.

This mixture is pressed at 95C for 20 minutes under a pressure of 5 kg/cm to form a compact board having a thickness of 3 mm and removed after cooling to 25C. The shaped article formed is then heated for 30 minutes at C in a press whose plates are 8 mm apart.

A porous material is obtained which after having been kept for 2-1 hours at 40C and 80? humidity is so flexible that it can be cut to sheeting having a thickness of 1.5 mm on a leather splitting machine.

After this porous sheet material has been conditioned at 23C and 50)? humidity. it gives an additional water vapor absorption of 260 g/kg upon being kept for 8 hours at 23C and 100C? humidity.

We claim:

1. A process for the production of sheet materials which absorb moisture vapor reversibly. which comprises applying an aqueous dispersion of a polymer. which contains polymerized units of at least 59 by weight of a tertbutyl ester of an ethylenieally unsaturated carboxylic acid at a pH of 1.5 or less to gas permeable sheet materials and heating at the decomposition temperature of the polymer to thereby eliminate an olefin and form free carboxylic groups in the polymer.

2. A process as set forth in claim 1 wherein said polymer is decomposed at a temperature of from 70 to C 3. A process as set forth in claim 1 wherein said polymer contains from 0.5 to 20% by weight of monomers selected from the group consisting of acrylic acid and acrylonitrile.

4. A process as set forth in claim 1 wherein said polymer contains from 0.1 to 10% by weight. based on the total weight of monomers. of polymerized units of an ethylenically unsaturated copolymerizable acid having a dissociation constant of more than 10.

5. A process as set forth in claim 1 wherein said polymer contains from 0.1 to 10")? by weight of monomers selected from the group consisting of vinylsulfonic acid. styrenesulfonic acid. 3-methacryloxypropylsulfonic acid. 3-methacryloxyethylsulfonie acid. 3- acryloxypropylsulfonic acid. 3-acryloxyethylsulfonic acid and vinylphosphonic acid.

6. A process as set forth in claim 1 wherein said polymer contains up to 957! by weight of comonomers selected from the group consisting of acrylic or methacrylic esters of alcohols having one to nine carbon atoms, vinyl chloride. vinylidene chloride. styrene. butadiene and vinyl esters.

7. A process as set forth in claim 1 wherein some or all of the carboxyl groups exposed by said thermal decomposition are neutralized by salt formation.

8. A process as set forth in claim 1 wherein a polyfunctional compound. the functionality of which will react with carhoxyl groups. is added to said polymer dispersion in an amount of from 0.5 to am by weight based on the amount of polymer used.

9. A process as set forth in claim 1 wherein a polyfunctional compound selected from the group consist ing of glycerol. glycol. and diglycol is added to said polymer dispersion in an amount of from 0.5 to 609% by weight based on the amount of polymer used.

10. A process as set forth in claim 1 wherein the carboxyl groups exposed by said thermal decomposition are reacted with a reactive polyfunctional compound.

11. A process as set forth in claim 1 wherein the carboxyl groups exposed by said thermal decomposition are reacted with hexamethylenediamine.

12. A process as set forth in claim 1 wherein the carboxyl groups exposed by said thermal decomposition are reacted with poly alent metal ions.

l3. A process as set forth in claim 1 wherein l to parts ofpoly inyl methyl ether is added to said polymer dispersion for every 100 parts of said polymer prior to use. and the coated sheet material is heated at a temperature of 50 to 200C for 5 to seconds prior to heating at said decomposition temperature. 

1. A PROCESS FOR THE PRODUCTION OF SHEET MATERIALS WHICH ABSORB MOISTURE VAPOR REVERSIBLY, WHICH COMPRISES APPLYING AN AQUEOUS DISPERSION OOF A POLYMER, WHICH CONTAINS POLYMERIZED UNITS OF AT LEAST 5% BY WEIGHT OF A TER-BUTYL ESTER IF AN ETHYLENICALLY UNSATURATED CARBOXYLIC ACID AT A PH OF 1.5 OR LESS TO GAS PERMEABLE SHEET MATERIALS AND HEATING AT THE DECOMPOSISTION TEMPERATURE OF THE POLYMER TO THEREBY ELIMINATE AN OLEFIN AND FORM FREE CARBOXYLIC GROUPS IN THE POLYMER.
 2. A process as set forth in claim 1 wherein said polymer is decomposed at a temperature of from 70* to 170*C.
 3. A process as set forth in claim 1 wherein said polYmer contains from 0.5 to 20% by weight of monomers selected from the group consisting of acrylic acid and acrylonitrile.
 4. A process as set forth in claim 1 wherein said polymer contains from 0.1 to 10% by weight, based on the total weight of monomers, of polymerized units of an ethylenically unsaturated copolymerizable acid having a dissociation constant of more than 10
 4. 5. A process as set forth in claim 1 wherein said polymer contains from 0.1 to 10% by weight of monomers selected from the group consisting of vinylsulfonic acid, styrenesulfonic acid, 3-methacryloxypropylsulfonic acid, 3-methacryloxyethylsulfonic acid, 3-acryloxypropylsulfonic acid, 3-acryloxyethylsulfonic acid and vinylphosphonic acid.
 6. A process as set forth in claim 1 wherein said polymer contains up to 95% by weight of comonomers selected from the group consisting of acrylic or methacrylic esters of alcohols having one to nine carbon atoms, vinyl chloride, vinylidene chloride, styrene, butadiene and vinyl esters.
 7. A PROCESS AS SET EXPOSED BY SAID THERMAL DECOMPOSITION THE CARBOXYL GROUPS EXPOSED BY SAID THERMAL DECOMPOSITION ARE NEUTRALIZED BY SALT FORMATION.
 8. A process as set forth in claim 1 wherein a polyfunctional compound, the functionality of which will react with carboxyl groups, is added to said polymer dispersion in an amount of from 0.5 to 60% by weight based on the amount of polymer used.
 9. A process as set forth in claim 1 wherein a polyfunctional compound selected from the group consisting of glycerol, glycol, and diglycol is added to said polymer dispersion in an amount of from 0.5 to 60% by weight based on the amount of polymer used.
 10. A PROCESS AS SET FORTH IN CLAIM 1 WHEREIN THE CARBOXY GROUPS EXPOSED BY SAID THERMAL DECOMPOSITION ARE REACTED WITH A REACTIVE POLYFUNCTIONAL COMPOUND.
 11. A process as set forth in claim 1 wherein the carboxyl groups exposed by said thermal decomposition are reacted with hexamethylenediamine.
 12. A process as set forth in claim 1 wherein the carboxyl groups exposed by said thermal decomposition are reacted with polyvalent metal ions.
 13. A process as set forth in claim 1 wherein 1 to 50 parts of polyvinyl methyl ether is added to said polymer dispersion for every 100 parts of said polymer prior to use, and the coated sheet material is heated at a temperature of 50* to 200*C for 5 to 60 seconds prior to heating at said decomposition temperature. 